Purpose :
to fully automate blood velocity and flow calculations from small microvessel (from 120µm down to 15µm) from imaging data acquired by the RFI

Methods :
Data analysis by the new software was carried out with eyes of more than 50 healthy and diseased subjects according to Helsinki approved standard protocols. Retinal images centered on the fovea were acquired with the RFI with a 20° filed (4.3x4.3mm2) or 35° (7.3x7.3 mm2). The RFI includes a fundus camera, fast stroboscopic flash to acquire short movies, and a 12 bits high resolution digital camera.

Results :
We completed the algorithms and the program for the fully automatic quantitative analysis, thus replacing the previous RFI’s semi-automatic procedure that was very good but time consuming. The new software carries out (i) Identifies and maps all vessels segments; (ii) Generates a topological map of the vessels (iii) Identifies which of the vessels are arterials and which are veins; (iv) Measures the diameter at every position (v) measures the average blood velocity for each segment (vi) Measures the average blood flow and (vii) prepare output summary of tables and images. The automatic calculations of all the above were very fast: On an Intel i7 4 core CPU the software run took 24 seconds per series of 8 frames from aligned images to calculation of ratio images via the above steps to the final results, or only 14 seconds from previous ratio frames measure during acquisition. The system often provided satisfactory results from only a single well focused series of 8 frames, acquired in ~120 milliseconds. We validated the new software by comparing with the performance of the semi-manual programs, after each program analyzed two groups of four independent series from the same eye. For the new software, the relative error in the mean velocity of the two independent groups of was 19.9% for veins, 24.4% for the arterial network and the average number of segments was 110, compared with the semi-automatic software results of 20.3%; 20.4% and n=65 respectively.

Conclusions :
To the best of our knowledge, the RFI system with its new fully automatic analysis software now outperform any alternative system for imaging and directly quantifying blood velocity and flow in small, retinal vessels, totally noninvasively, in a clinical setting.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.